A gel can be applied to a skin of a subject to improve transmission of energy emitted by devices such as but not limited to, an ultrasound device (e.g., a Transcranial Doppler (TCD) device). The gel can be initially applied manually by an operator or automatically by the device in any suitable manner. In some situations, the gel may be lacking in some areas of the scanning surface for various reasons (e.g., due to the device spreading the gel during operation). Accordingly, an area that is covered by an insufficient amount of gel may degrade the performance of the device (e.g., by failure of transmission of energy waves).